Earthquake early warning systems are working in recent years. The earthquake early warning systems, upon occurrences of earthquakes, analyze data that are observed by seismographs installed at points near focuses of the earthquakes, estimate the focuses of the earthquakes and the magnitudes of the earthquakes, and predict seismic intensities and the arrival times of tremors at the respective points on the basis of the results of the estimations.
Upon occurrence of an earthquake, a small tremor (a longitudinal wave) called a minor initial tremor, or a primary wave (P wave), and a large tremor (a transverse wave) called a principal motion, or a secondary wave (S wave), occur at the focus of the earthquake. The propagation velocity of the P wave is about seven km/sec while the propagation velocity of the S wave is about four km/sec.
In such an earthquake early warning system, the behavior of the S wave is predicted, by utilizing difference in the propagation velocities between the P wave and the S wave, based on the observation data about the P wave at points near the focus of the earthquake. Accordingly, for example, at a point apart from the focus of the earthquake by a certain distance or more (at a point where there is a large difference between the arrival times of the P wave and the S wave), it is possible to predict the magnitude of the earthquake and the arrival time of the tremor before the S wave arrives at the point.
For example, as illustrated in FIG. 1A, upon occurrence of an earthquake, out of the P wave and the S wave that have occurred at the focus of the earthquake, the P wave is observed by a seismograph 200 prior to the S wave. Data about the P wave observed by the seismograph 200 is transmitted to, for example, a National Weather Service 100.
The National Weather Service 100 estimates, for example, the focus and the magnitude of the earthquake based on the data observed by the seismograph 200, and predicts the seismic intensity and the arrival time of the tremor in each area based on the result of the estimation.
As illustrated in FIG. 1B, earthquake early warning including information concerning, for example, the seismic intensity and the arrival time of the tremor in each area, which are predicted by the National Weather Service 100, is transmitted to a system user, such as a cell broadcast center (CBC) 300. Thereafter, for example, earthquake information generated based on the earthquake early warning is secondarily distributed to each end user by the CBC 300.
For example, in a typical third-generation (3G) communication system, the earthquake early warning is transmitted from the National Weather Service 100 to the CBC 300 upon occurrence of an earthquake. The CBC 300 determines a distribution area of the earthquake information, based on the information concerning, for example, the seismic intensity and the predicted arrival time of the tremor in each area, which is included in the received earthquake early warning, and generates the earthquake information to be distributed to users in the distribution area. Then, the CBC 300 transmits the generated earthquake information to a serving General Packet Radio Service (GPRS) support node (SGSN). The SGSN receives the earthquake information transmitted from the CBC 300 and notifies mobile stations (MSs) in the distribution area of the received earthquake information via a radio network controller (RNC) and a base station (BS).
For example, in a typical Long Term Evolution (LTE) communication system, the earthquake early warning information is transmitted from the National Weather Service 100 to the CBC 300 upon occurrence of an earthquake. The CBC 300 determines a distribution area of the earthquake information, based on the information concerning, for example, the seismic intensity and the arrival time of the tremor in each area, which is included in the received earthquake early warning, and generates the earthquake information to be distributed to the users in the distribution area. Then, the CBC 300 transmits the generated earthquake information to a mobility management entity (MME). Each eNodeB (eNB) arranged in the LTE communication system receives the earthquake information from the MME and notifies the MSs in the distribution area of the earthquake information.
Methods of distributing the earthquake information include a Cell Broadcast Service (CBS) method and an Earthquake and Tsunami Warning System (ETWS) method.
For example, Japanese Laid-open Patent Publication No. 2010-245702 proposes a communication apparatus that behaves in accordance with a disaster scenario that identifies the status of a disaster. Japanese Laid-open Patent Publication No. 2008-61196 proposes a system that extracts a path that is disconnected on the basis of any fault portion that has been caused upon occurrence of a disaster to build a bypass path of the extracted disconnected path.